Lighting systems having a power source, structural and power connections to one or more light sources are widely used in industrial, commercial and domestic environments. Since these electrical systems may be extended and carry substantial amount of alternating current, substantial amount of electromagnetic ("EM") radiation may be generated. The EM radiation may interfere with the operation of co-existing electrical or electronic appliances. Therefore, regulatory authorities in various countries have mandated the maximum amount of EM radiation an electrical appliance may emit in a specified environment.
With the advent of the high efficiency light sources such as those using low voltage halogen lamps, the problem of EM interference becomes more acute. Many of these light sources operate with a much lower operating voltage than line voltage. A voltage converter or transformer is required to change the line voltage to the lower operating voltage. The conversion process often results in the generation of EM interference signals. This is particularly true for low-cost electronic voltage converters operating under the principle of power switching. The switching rate is typically in the radio frequency portion of the EM spectrum. Also, the lower operating voltage requires a higher operating current to maintain a given power output. The higher operating current also results in a higher emission of EM interference signals.
FIG. 1 illustrates schematically a top view of a conventional lighting system 10. The lighting system 10 is typically hung from a ceiling or mounted on a stand. It has a number of low voltage lamps 20 attached to and commuting with a pair of rails 30. The pair of rails are usually fashioned out of chrome plated copper or steel rods extending from a housing 40 and may terminate with a non-conducting, decorative end bar 32. The housing 40 houses a power supply which is typically a transformer or a voltage converter 50. The voltage converter 50 converts a line voltage such as 110 or 220 V AC at 50 or 60 Hz to a substantially lower voltage, e.g., 12 VAC, at a substantially higher frequency, e.g., 20 kHz. The voltage converter 50 outputs this lower voltage at higher frequency to electrify the pair of rails 30. The lamps 20 each has a pair of leads 22 that makes electrical contact with the pair of rails.
FIG. 2 shows a partial, perspective side view of the conventional lighting system 10 of FIG. 1. Since the rails 30 of the lighting system 10 carry high frequency and high current electrical power, they act as antennae emitting radio frequency EM emissions. These high frequency emissions interfere with the operations of surrounding electronics such as televisions, telephones, radios and computers.